1. Field of Invention
The invention relates to a packaging structure and a manufacture method and more particularly to a wafer level packaging structure with inductors and manufacture method thereof.
2. Related Art
An inductor is a kind of passive device, which is also known as coil. The inductor is a component, which is coiled with a conducting wire to have an inductance property. By changing the current going through the coil, the coil will have a different magnetic flux. Usually, an inductor having a single coiled conducting wire will have self-inductance and an inductor coiled with more than one conducting wire will have mutual-inductance. The main purpose of an inductor is to prevent the interference of an electromagnetic wave, to shield the electromagnetic wave radiation or to filter the noise of the current. An inductor is widely applied in power supply, monitors, converters, motherboards, scanners, telephones or modems.
Besides, an inductor is often integrated in a semiconductor substrate in order to reduce the production cost of small and high integrity components for a wireless communication product. Radio frequency (RF) inductance is widely used in an RF module for wireless communication. When the frequency of a carrier wave is getting higher and higher, the demand for an inductance with a high quality factor is also increasing.
Insufficient quality is the biggest problem of integrating an inductor in a semiconductor substrate. The efficiency of the inductor in the semiconductor can not be as good as an ideal inductor because a coil has impendence loss during the metallization process, and because of the impendence of the semiconductor substrate and the capacitance, which is coupled to the substrate. Usually, a quality factor is used for estimating the efficiency of an inductor. In order to reduce the loss, have the highest quality factor, and comply with the semiconductor process at the same time, the inductor coil must be made of a metal, which has low impendence loss. In addition, in order to reduce the loss caused by the eddy current of the semiconductor substrate and reduce the capacitance, which is coupled to the substrate, the inductor coil should stay away from the substrate as far as possible.
Thus, in order to improve the inductor quality factor, U.S. Pat. No. 5,844,299 disclosed an integrated inductor, which was formed by etching a cave on the substrate, depositing a dielectric material group in the cave, forming a dielectric layer on the dielectric material group and forming a conducting coil on the dielectric layer, such that the parasitic effects and the energy loss of the substrate can be reduced by intervening the dielectric material group and the dielectric layer between the coil and the substrate. In addition, U.S. Pat. No. 6,008,102 disclosed an integrated inductor, which had a coil with three-dimensional structures. The three dimensional structure was formed by multiple photography, etching and metal material depositing processes. The inductor coupling effects between the three dimensional coils can restrain the magnetic field so that low reactance can be retained and a self shielding effect can be created to improve the inductor quality factor.
Moreover, the energy loss caused by the substrate can be reduced by using an etching process to excavate some parts of the substrate and support an inductor by some holders. For example, U.S. Pat. No. 6,495,903 disclosed an integrated circuit inductor including a spiral aluminum coil, which was deposited on an oxidation layer of a silicon substrate. The silicon substrate had been excavated to form an air hole, which is below the coil to provide a low dielectric constant medium, such that the impedance of the substrate and the capacitance, coupled to the substrate, can be reduced. However, the process of forming an air hole below the metal coil after depositing the metal coil, in order to use the oxidation layer to support the metal coil, needs complex and more etching processes. U.S. Pat. No. 6,835,631 disclosed an inductor manufacturing process, which can improve the inductor quality factor. The process included forming a first oxidation layer on a substrate, forming a low dielectric constant layer on the first oxidation layer and forming a second oxidation layer on the low dielectric constant layer. Next, an air gap was formed by etching the second oxidation layer and the low dielectric constant layer. An upper low dielectric constant layer was then formed. Finally, an inductor was formed in the upper low dielectric constant layer, which was above the air gap. The process also needed etching processes in order to form air gaps for improving the inductor quality factor.
In summary, the quality of an integrated inductor in the semiconductor substrate is not good because of the impendence of the substrate and the capacitance coupled to the substrate. Therefore, in order to isolate the inductor coil from the substrate to reduce the inference, an air medium is necessary between the coil and the substrate. However, the present processes to provide the air gap or air hole are all involved etching processes, which are more complex, such, that the yield is hard to improve.